Disable coverage as cargo-llvm-cov depends on rust nightly

Nightly no longer compiles difftastic due to a rust issue with
linking: https://github.com/rust-lang/rust/issues/95561

.github/workflows/coverage.yml

@@ -1,22 +1,22 @@
-name: Coverage
+# name: Coverage
 
-on: [pull_request, push]
+# on: [pull_request, push]
 
-jobs:
-  coverage:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup toolchain install nightly --component llvm-tools-preview
+# jobs:
+#   coverage:
+#     runs-on: ubuntu-latest
+#     steps:
+#       - uses: actions/checkout@v2
+#       - name: Install Rust
+#         run: rustup toolchain install nightly --component llvm-tools-preview
 
-      - name: Install cargo-llvm-cov
-        uses: taiki-e/install-action@cargo-llvm-cov
+#       - name: Install cargo-llvm-cov
+#         uses: taiki-e/install-action@cargo-llvm-cov
 
-      - name: Generate code coverage
-        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
-      - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v1
-        with:
-          files: lcov.info
-          fail_ci_if_error: true
+#       - name: Generate code coverage
+#         run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+#       - name: Upload coverage to Codecov
+#         uses: codecov/codecov-action@v1
+#         with:
+#           files: lcov.info
+#           fail_ci_if_error: true